1. Field of the Invention
The present invention relates to a position detection apparatus and an exposure apparatus and, more particularly, to a detection apparatus for detecting the position of a mark formed on an object placed on a stage, and an exposure apparatus including the apparatus.
More specifically, the present invention is preferably applied to an apparatus for detecting the relative positional relationship between a pattern on an object such as a wafer and a stage on which the object is placed, or the relative positional relationship between the pattern on the object and a pattern on a mask such as a reticle when the pattern formed on the mask is to be transferred to the object.
The present invention is also preferably applied to an apparatus for manufacturing semiconductor devices such as ICs or LSIs, image sensing devices such as CCDs, display devices such as liquid crystal panels, or devices such as magnetic heads, and for example, to a proximity exposure apparatus, a projecting exposure apparatus (a so-called stepper), or a scanning exposure apparatus.
2. Description of the Related Art
In an exposure apparatus (e.g., a stepper) used to manufacture semiconductor elements, a pattern formed on a mask such as a reticle is projected onto a substrate such as a wafer through a projecting lens, thereby transferring the mask pattern to the substrate. To make the pattern to be transferred match the pattern already formed on the substrate, the position of an alignment mark formed on the substrate must be detected using an observation unit (e.g., an off-axis scope), and positioning (alignment) between the mask pattern and substrate pattern must be done on the basis of the detection result.
The position of the observation unit (e.g., an off-axis scope) is fixed. For this reason, to detect the position of the alignment mark, the stage must be driven to move the alignment mark on the wafer to the mark observation position (position where the position of the alignment mark can be detected by the observation unit).
After the positions of the stage in the X, Y, and θ directions are accurately measured by laser interferometers, the stage is moved to an arbitrary target position on the basis of the measurement result. In observing an alignment mark, generally, non-exposure light is used to minimize damage to the wafer.
The non-exposure light that irradiates the alignment mark and is reflected by the mark is sensed by an image sensing unit such as a CCD camera and received by the control unit of the exposure apparatus as an image signal. The position of the mark is detected by processing the image signal by the control unit.
When the mark is to be observed by an off-axis scheme such as the TTL off-axis scheme, wafer alignment can be performed by a global alignment scheme (AGA) including the above-described alignment mark measurement process.
In global alignment, the stage is driven to sequentially move alignment marks in predetermined shots to the mark observation position, and the alignment marks are observed by an observation unit. The step amount of the stage is corrected on the basis of the measurement results, i.e., alignment mark alignment/misalignment in all shots.
As advantages of this alignment scheme, measurement results that are obviously abnormal can be excluded from the alignment mark position measurement results, and since a plurality of measurement results are used, the reliability of the determined rotation and magnification components becomes high because of the averaging effect. When the rotation and magnification components are accurately measured by this alignment scheme, and the step amount of the stage is properly corrected, alignment errors during exposure become almost zero.
In observing an alignment mark on a wafer, the stage is driven. Especially, since alignment marks of a plurality of shots are observed in global alignment, the stage must be driven a number of times. To improve the throughput, every time the alignment mark in one shot is sequentially moved to the mark observation position, the stage must be quickly accelerated and stopped.
When the stage is driven to the mark observation position and stopped, processing waits until swing of the stage settles to a predetermined allowable range (tolerance). After this, an image signal is obtained by the CCD camera to measure the position of the alignment mark. However, when the stage is quickly accelerated and stopped, the entire exposure apparatus may swing, and a long time may be required for swing (variation) of the stage to subside.
In this case, the image signal obtained by the CCD camera contains the influence of a small swing (variation) of the stage during the image signal reception period. As a consequence, the alignment mark measurement result contains errors due to swing of the stage.
A projecting exposure apparatus has a mount system for settling swing of the apparatus main body due to step movement of the stage. When this mount system is adjusted, swing of the entire projecting exposure apparatus can be suppressed to some degree. However, when the mount system is adjusted to suppress swing caused by quick acceleration and stop of the stage, the stage may readily swing due to the influence of swing of the floor. Hence, conventionally, after the stage comes to a complete halt, an image signal is obtained by the CCD camera to measure the position of an alignment mark. As a result, the throughput cannot be improved conventionally.